Frangible elements in sheet material

ABSTRACT

A frangible element or weakened line in sheet material, especially tinplate, which is useful in opening means for containers. A method and apparatus for making the line is described. The frangible element lies between two portions of the sheet of greater thickness than the frangible element, to which it is joined by rounded steps or other rounded formations, and a hollow indentation, e.g., a bead, lies in one of the portions. By using a series of indentations, these can be arranged so that the opening of a tear-open panel in the container wall can be controlled more easily.

United States Patent Cookson Oct. 17, 1972 [54] FRANGIBLE ELEMENTS INSHEET [58] Field of Search ..220/54, 27, 48; 113/15 A MATERIAL [72]Inventor: William Cookson, Fareham, En- [56] References cued glandUNITED STATES PATENTS [73] Assignee: Cookson Sheet "Metal Developments3,434,623 3/ 1969 Cookson ..2 20/54 Limited, Southampton, England3,478,918 11/1969 Zundel ..220/54 [22] Filed June 24 1971 3,490,6431/1970 Henning et al. ..220/54 211 App]. No.: 156,294 PrimaryExaminer-George Tfl-lall R I t d U S A r r ta Att0rney-Howard J.Churchill et al.

eae pplcalon a [63] -Continuation-in-part of Ser. No. 796,975, Feb.[.57] ABSTRACT a continuatiozn'in'part 0f A frangible element orweakened line in sheet materi- 23,330,AP"115,197O- al, especiallytinplate, which is useful in opening a means for containers. A methodand apparatus for Foreign Application Priority Data 7 making the line isdescribed. The frangible element lies between two portions of the sheetof greater h l t ..7, 68 2:2 4 gig: 4 2231 thickness than the frangibleelement, to which it IS 1970 Great Britain 6335/7O joined by roundedsteps or other rounded formations, J 1971 tB "28024/7l and a hollowindentation, e. g., a bead, lies in one of 5 l970 i i 58/70 theportions. By using a series of indentations, these 1970 "10545 can bearranged so that the opening of a tear-open ustrala panel in thecontainer wall can be controlled more '1 52 us. Cl. ..220/27, 220/48,220/54 y a [51 Int. Cl ..B6Sd 17/00, 365d 17/20 30 Claims, 15 DrawingFigures PATENTED Hill 1 7 I972 SHEET 8 BF 5 FRANGIBLE ELEMENTS IN SHEETMATERIAL This application is a continuation in part of U.S. applicationSer. No. 796 975 filed Feb. 6, 1969 and allowed Mar. 29, 1971 and ofU.S. application Ser. No; 28,880 filed Apr. 15, 1970 and allowed Apr. 5,1971, the latter application being itself a continuation in part ofapplication Ser. No. 796, 975.

This invention relates to sheet material, especially thin sheetmaterial, provided with a frangible element.

It further relates to containers including such sheet material, and tomeans for the easy opening of con- 7 tion, a rounded step in the topsurface of the first por- I tainers. It is particularly applicable tocontainers made of thin sheet material, for example tinplate, in which aportion of the material bordered byv a weakened line is torn by handfrom a wall or end of the container.

It is the usual practice to provide a weakened line in sheet metal byscoring, that is by pressing a top die having a sharpened edge on to aflat bottom die to partially cut through the sheet metal to leave aresidual of metal of about percent of the original thickness of thematerial.

As the displaced metal flows from each side of the scoring tool it formsinclined surfaces in the top portion of the metal causing compressionstresses which are unbalanced between the top and bottom surfaces of themetal. In consequence, the stresses induce work hardening of theresidual metal below the scoring tool which inhibits the metal flow andthis can give rise to incipient cracks. Because of these factors it hasbeen found difficult to maintain a scored line with a residual of theconsistent depth necessary for the ready tearability of easy open lidsparticularly when these are made from tinplate.

Problems in maintaining the tooling arise particularly when scoringtinplate because the edge of the scoring tool requires replacing atfrequent intervals as it becomes blunted by the impact of the tool onthe surface of the tinplate supported by the bottomdie.

When using tinplate the scoring process is often not deemed to besatisfactory as the scoring tool cuts through the coating of tin on thesheet metal which gives rise eventually to corrosion. To overcome thisproblem a coating of lacquer is usually applied to' the material, whichis an additional expense in manufacture.

It is an object of the present invention to provide sheet materialhaving a weakened line or weakened portion especially sheet metal with afrangible element suitable for use in a container wall.

Another object is to provide sheet material having a frangible elementwhich can be made with less likelihood of cracks forming in or adjacentthe frangible element than has been the experience hitherto. Anotherobject is to provide plated sheet material (for example tinplate) havingsuch a frangible element which can be made in such a way as to avoidcutting through the plating. It is a further object to provide sheetmaterial with a frangible element arranged to form a tear-open panelwhich can be controllably opened.

According to one aspect of the present invention sheet material whichcan be made in such a way as to overcome or assist in overcoming theformation of cracks and in such a way that the plating (if the materialis plated) remains unbroken in and adjacent the frangible element ischaracterized by having a first portion of the sheet leading to afrangible element comprising material of smaller thickness than thefirst portion, a rounded formation in a surface of the sheet leadingfrom the frangible element to a second portion of the sheet material,the second portion having a thickness greater than that of the frangibleelement and having'formed therein at least one hollow indentation. Asexplained more fully in my co-pending patent application filed on thesame day as this application, and entitled Improvements in or relatingto the manufacture of a frangible element in sheet material such sheetmaterial may be made by means of press tool dies, excess material fromthe thinned portion passing, during the pressing operation into the saidsecond portion of the material.

The rounded formation may be a downward formation, an area of the secondformation adjoining the thinned portion being planar except for adeformation therein formed between substantially parallel curveddepressions in the surfaces close to the thinned portion.

The deformation in the second portion of the sheet may be a hollow beadadjoining the frangible element, and the rounded deformation may leaddirectly into the head, for example, there may be a downward formationleading to a downwardly formed bead or an upward formation leading toanupwardly formed bead. Alternatively the rounded formation may be astep leading to a planar area, the bead or other indentation beingadjacent to the frangible element but separated therefrom by the planararea.

In one of its aspects, sheet material according to the invention hassheet material having a first portion, a downward formation in-the topsurface of the sheet leading to a frangible element comprising materialof smaller thickness than the first portion, the downward formation inthe bottom surface of the sheet leading from the frangible element to asecond portion of the sheet material, the second portion having athickness greater than that of the frangible element and having formedtherein a hollow bead close to the frangible element.

It is preferred that the thickness of the frangible element shall beless than half (and preferably about onethird or even less) of thethickness of the first and second portions of sheet material.

A principal use of sheet material having a frangible element is toprovide a tear-open panel in a container. wall. A container wall in oneaspect of my invention is formed of sheet metal having a thinned portionof a width greater than its thickness comprising a frangible elementbounding a tear-open panel, an elongate deformation in the tear-openpanel extending alongside and close to the thinned portion comprisingsubstantially parallel curves in the two surfaces of the tear-openpanel. A handle is preferably secured to the tear-open panel of the wallso that the thinned portion can be ruptured and the tear-open panellifted from the wall. To facilitate the rupture of the thinned portion,the handle may be hinged to allow initial downward puncture of thethinned portion on lifting the handle.

As already indicated, the hollow indentation of or indentations may bedownwardly formed or upwardly formed. I have discovered that, if thereis provided in the sheet material a series of hollow beads, these may beused to assist in opening a tear-open panel in a container wall.

Thus according to another aspect of this invention there is providedsheet material having a first portion, a downward formation in the topsurface of the sheet leading to a frangible element comprising materialof a smaller thickness than the first portion, a second portion ofthickness greater than that of the frangible element joining thefrangible element on the other side from the first portion, and a seriesof beads or indentations in the second portion. The sheet material maybe used for a container wall, the frangible element forming part ofopening means for the container wall and bordering a tear-open panel forthe wall, the series of beads or similar shapes within the panelassisting in the controlled removal of the panel by means of an openingdevice, e.g., a handle secured to the tear-open panel by providingspaced areas of stiffening in the panel preferably parallel to thefrangible element. In this aspect of the invention, when the frangibleelement is broken through and the tear-open panel pulled away, the sheetmaterial bends along successive lines across the sheet between the beadsto allow controlled removal of the panel.

In one form a single elongate bead is provided either close to oradjacent the frangible element, extending continuously for the whole orpart of the length of the frangible element and a series of separatebeads or indentations (preferably a series of beads parallel to thesingle elongate bead) is formed in the second portion on the oppositeside of the single bead from the frangible element. The beads orindentations (including the elongate bead if present) may be formedupwardly or downwardly and need not all be formed in the same direction.The said separate beads may all be the same distance from the frangibleelement and may be equally spaced from one another. Where an elongatehead as aforesaid is downwardly formed a downward formation in thebottom surface of the material may lead from the frangible element. intothe elongate bead. In a very similar manner, if the elongate bead isupwardly formed, an upward formation may lead from the frangible elementinto the elongate bead.

In another form of the invention in place of an elongate bead a seriesof beads is formed close to the frangible element. If these beads areformed downwardly, a downward formation in the bottom surface of thematerial at the edge of the frangible element may be formed by theseries of beads, and between the beads a downward step in the material.If the beads are formed upwardly an upward formation may lead from thefrangible element into the outer surface of each bead.

The beads or indentations in the sheet material may be so arranged as togive in the material a plurality of substantially parallel lines of lowresistance to flexing separated by areas of relatively high resistanceto flex- When the sheet material is made up into a container wall forthe purpose of allowing the frangible element to be broken through bysuitable means to bend back a portion of the material defined by thefrangible element, the series of beads or indentations may be sopositioned that the act of bending back the portion of material causesthe sheet material to bend along successive lines across the sheetbetween the beads or indentations. This enables a greater control to beexercised over the bending operation.

In the description with reference to the drawings the invention isexemplified as applied to tinplate and it is with this material andother plated materials particularly that the advantages of the inventionare obtained. However the claims are not limited to the use of tinplateas the sheet material, because the invention is applicable to othermaterials. I

Various forms of this invention will be described with reference to theaccompanying drawings in which:

FIG. 1 illustrates in part perspective a weakened line made in sheetmetal by scoring means of a type employed prior to the presentinvention;

FIG. 2 illustrates in part cross-section view dies for providing ascored line in sheet metal as shown in FIG.

FIG. 3 illustrates in part perspective view a weakened line or frangibleelement in sheet metal according to the present invention; I

FIG. 4 illustrates in fragmentary cross-section view dies for formingthe weakened line or frangible element shown in FIG. 3, in the openposition;

FIG. 5 illustrates in fragmentary cross-section view the dies shown inFIG. 4 in the closed position;

FIG. 6 illustrates in fragmentary cross-section view a view similar tothat of FIG. 5 showing a recessed top die;

FIG. 7 illustrates in fragmentary cross-section view means forreinforcing a thinned portion;

FIG. 8 illustrates in part perspective view a preferred form of openingdevice for a container lid using a frangible element similar to thatshown in FIG. 7; and

FIG. 9 illustrates in fragmentary cross-section view the container lidshown in FIG. 8 being opened.

FIG. 10 illustrates in part perspective view a weakened line orfrangible element in sheet metal according to the present invention withintermittent beads adjacent to a first bead; I

FIG. 11 illustrates in part perspective view a weakened line orfrangible element in sheet metal with a series of intermittent beadsadjacent to the frangible element;

FIG. 12 illustrates a part cross-section through a sheet metal containerhaving a lid consisting of a sheet metal member such as shown in FIG.11, the section being taken along one of the lines 1'70 of FIG. 11;

FIG. 13 illustrates in perspective view a panel of the lid shown in FIG.12 being removed from the container.

FIG. 14 is part perspective view showing a weakened line or frangibleelement in sheet metal with a series of upwardly formed beads; and

FIG. 15 is a part cross-section similar to FIG. 14 but showing theseries of beads closer to the frangible element.

In FIG. 1 is shown a lid 10 of, for example, a container made of sheetmetal having a weakened line 12 made by scoring or partially cuttingthrough the metal in accordance with a previous method.

FIG. 2 illustrates the dies used to make the scored line 12 in FIG. 1.The sheet metal lid 10 is located between a scoring tool 14 and an anvil16 with the sharp edge 18 of the scoring tool 14 entering into the sheetmetal. Penetration of the metal by the scoring force 20 is resisted bycompressive stresses 21 in the top portion of the metal. The displacedmetal forms inclined surfaces in the top of the metal on each side ofthe scoring tool resulting in unbalanced stresses between the top andbottom surfaces of the metal so causing failure in the form of cracks,22.

In FIGS. 3, 4, and 5 there is shown in accordance with the presentinvention an article and a method and apparatus for making it, thearticle comprising a sheet metal container wall 26, in this instance atinplate lid, having a weakened line or frangible element 24. Thefrangible element 24 bounded by steps forms part of an extrusion in themetal, the formation of which is subsequently described, the extrusiondefining a tear-open geometric pattern (surrounding a tear-open panel)and being, in this example, annular in plan. The frangible element 24 isin the form of a thinned portion of the metal constituting an area ofthickness smaller than the general, substantially uniform, thickness ofthe container wall 26, and is elongated inwardly from the peripheralbounds of the geometric pattern, having a controlled cross-section ofessentially constant thickness.

In FIGS. 3, 4, and 5 the annular frangible element 24 is made bypressing an annular portion of the metal which with an annular hollowbead 30 bounds a central area 32 of the lid 26. The lid which has a rim34 before making the weakened line, is shown in open press tool dies inFIG. 4. The dies are made from suitable tool material and they comprisea top die 36 and a bottom die 40. The dies 36 and 40 are generallycircular. A part of the left-hand side only of the dies is shown inFIGS. 4 and.5 along a radial section line. The-shape towards the centerof the dies may be modified as shown in FIG. 7 subsequently described.

Top die 36 has a flat surface 42 comprising two concentric areas 42a,42b separated by a projection in the form of a bead 47. The top die hasa raised stepped edge portion 44 including a step 46 and a flat surface48. The step 46 has rounded edges 49,49 where it joins the surfaces 42b,48. A step joining surfaces'through curved or rounded edges in dies orsheet material is referred to in this description and the claims as arounded step. Such steps between the curved or rounded edges may beperpendicular to the surfaces they join or inclined to one or both ofthem. Surfaces 48 and 42b which are parallel comprise respectively topand bottom work-contacting surfaces for the top die separated by therounded step 46 and surrounding a central area ofthe die.

Bottom die comprises a rim portion 50 and a flat portion 52 constitutinga work-contacting surface which extends inwardly of rim portion 50 to anedge or step 56 from where on the bottom die is relived to allowdownward displacement of the sheet material. In detail, adjacent flatportion 52 is provided a stepped portion 54 and a recess 60. The steppedportion 54 comprises a rounded step 56 and a ledge 58 underlying theflat surface 42b of top die 36. Step 56 joins surfaces 52, 58 throughrounded edges 59, 59. Ledge 58 comprises a further (bottom)work-contacting surface for the bottom die separated by the step 56 fromthe (top) workcontacting surface 52 and with it surrounding a centralarea of the bottom die. Flat portion 52 and ledge 58 are jacent to theledge 58 of stepped portion 54 is provided the recess 60. It will beobserved that the bead 47 of the top die isopposite the recess 60, i.e.,at a position to register with the recess for the purpose subsequentlyexplained. It should be understood that the designations top and bottomin relation to the dies described and claimed herein are not intended toindicate that one die will always be used vertically above the other.

Any suitable orientation of the dies may be used. The designations topand bottom in relation to the surfaces of the sheet metal should besimilarly understood.

Referring to FIG. 4,- as the top die 36 moves towards the bottom die,the bead 47 initiates a deformation in the sheet metal in the shape of ashallow curve at the point where the bead impinges on the metal.Subsequently as the dies close further, (FIG. 5) the'top die 36cooperates with the bottom die 40 to complete the formation of thesubstantially part-circular bead 30 from this deformationand to displaceparts of the sheet metal to different planes and to form a thinnedportion 24 or frangible element between work-contacting surfaces 42b and52. It will be seen that a part of the top surface of the material isdisplaced by the dies towards an opposite side of the sheet and a partof the bottom surface of the sheet is displaced in the same direction.Edges 64, 66 of the two displaced parts are separated with the thinnedportion 24 in between. A downward formation in the shape of a roundedstep 64 is produced in the top surface of the sheet leading from a firstportion 65 of the sheet to the thinned portion 24 which is in a planeparallel to the first portion 65 and of smaller thickness than the saidportion. A downward formation or depression in the shape of a roundedstep 66 is also formed inthe bottom surface of the sheet leading fromthe thinned portion to a second portion 67 of thickness greater than thethinned portion. Steps 64 and 66 are formed in the same direction andare spaced from each other with the frangible element 24 between them.These steps correspond to the step 46 in the top die and the step oredge 56 in the bottom die, which, as shown, are spaced apart in theclosed position of the dies.

In the pressing operation, the bead 47 of top die 36 presses the sheetmetal of the lid 26 into recess 60 of bottom die 40, drawing metal downinto the recess while a portion of flat surface 42b of top die 36compresses and thins the sheet metal against the flat portion 52 ofbottom die 40 over the area of overlap between these two work-contactingsurfaces. The thinned area comprises the weakened line or frangibleelement 24 its edges being defined by steps 64 and 66. Step 66 liesinwardly of step 64 substantially parallel thereto. The width of thefrangible element 24 is substantially constant and is greater than itsthickness. The

steps are annular in form as is the frangible element.

The formation of the thinned portion 24 and the bead 30 may beconsidered as an inward extrusion of the material between the dies, thefinal shape of which is controlled by the shape of the dies. The inwardmovement of the material is facilitated by the rounded edges 49, 49, 59,59' of the steps in the dies which assist and control the flow of thematerial. This flow of material and the means for producing it are quitedifferent from scoring as abovedescribed and are also quite differentfrom semi-shearing in which metal is partially cut through or sheared byuse of sharp cornered tools,

which moreover do not compress. a portion of metal to thin it.

Referring to FIG. 3, the metal sheet in the region of the extrusion isseen to have on the top surface first and second surface elements a andb in different planes joined by a step 64 (corresponding to the top diesurfaces) and a curved surface element c adjacent the second saidelement directed away from the plane of the first element a. On thebottom surface the metal sheet has (corresponding to flat portion 52 ofthe bottom die) a plane surface element '11 opposite the first surfaceelement a and the step 64 and also opposite at least part of the secondsurface element b and a curved surface e opposite and substantiallyparallel to the curved surface c on the top surface of the sheet, thedistance between the first surface element a and the plane surfaceelement d exceeding the distance between the second surface element band the plane surface element d. The plane surface element d joins thelower curved surface e by a step 66 directed away from the plane of thesecond surface element b, and a ledge f. Drawing the sheet metal to formbead 30 from the area of the frangible element 24 assists inaccommodating the excess metal which freely flows inwardly in the diesfrom the thinned area to produce a deformation in the lid in acontrolled manner. If the deformation was not initiated by theprojection in the die 36, there would be a danger of it taking place atrandom across the lid producing undesired buckling. The thickness of themetal in the area of the bead 30 between the curves and e remainssubstantially the same during the process of deformation.

While it is not desired to be bound by theory it is believed that thecompression stresses 68 (FIG. are equally balanced between the top andbottom surfaces of the sheet metal so the displaced metal can flow inequilibrium between the dies into the bead 30 without any or withreduced risk of work hardening the thinned metal so avoiding or reducingthe risk of cracking. The method and apparatus facilitate the productionof a consistently accurate depth of residual material in the lid orother container wall which ensures that this can always be readily andeasily opened by the user by use of suitable means, e.g., assubsequently described. The residual thickness is preferably less thanhalf the general lid thickness. For tinplate lids 0.009 ins. thick theresidual material is preferably approximately one third this thickness,i.e., 0.003 ins. thick. The residual depth can be varied according tothe characteristics of the material.

Repeatable accuracy of depth of the frangible element is obtained oververy large production runs as the flat work-contacting surfaces maintaintheir shape and form. This overcomes the disadvantage arising from priorart scoring processes where constant impact of the scoring tool on-theanvil causes the tool to become blunt.

In a modification of the dies shown in FIGS. 3 to 5, the step 56,rounded at 59, leads downwardly directly into a recess similar to recess60, the work-contacting surface 58 being omitted. A step similar to step64 is thereby formed in the upper surface of the sheet material while onthe bottom surface, a depression is formed in the recess adjoining thethinned portion or frangible element. This depression provides the lowersurface of a bead which is formed in the recess by a cooperating bead inthe top die.

Referring now to FIG. 6 there is shown a section through dies and a lidgenerally similar to the dies shown in section in FIG. 5, like partsbeing indicated by like numerals. The section is taken along a linewhere upstanding triangular shaped cars for use subsequently as securingmeans have been formed in the central area 32 of the lid 26 prior to itsentry into dies 36, 40. The triangular shaped ears extend generallyparallel to the rim 34 of the lid 26 preferably along an arcuate lineinwardly of and parallel to a part of the circumference of the lid. Theears have-a channel 72 between them which is intended to receive fixingtabs of a handle used in opening means for the container. A recess 74 intop die 36 provides a clearance right around the lid to clear channel 72and a bead similar to bead 116 subsequently described with relation toFIG.

In the present exampleit is convenient to form the ears 70 in the blankprior to making the frangible element to avoid breaking the element in asubsequent forming operation. The ears may be used to make a foldedconnection 76 described later in relation to FIG. 8 by placing tabs 78of an opening device 80 into the channel 72 and bending down the earsover the tabs while holding the remainder of the lid in suitable clamps.

In FIG. 7 is shown a form of reinforcement for a can end made, forexample, of tinplate formed adjacent a thinned weakened portion orfrangible element 98. A lid 84 has in the base of its rim 86 areinforced edge 88 comprising two layers of material overlying thematerial 89 adjacent the thinned portion 98, the layers being joined toeach other and to the material 89 through reversed bends 90 and 92. Bend90 provides adjacent one of the rounded steps 96 which bounds thethinned portion a shoulder 94 against which can be broken an edge 97 ofthe thinned portion. Shoulder 94 also provides a safe edge for theinside of the container when the removable portion 100 of the lid hasbeen removed. A bead 102 is provided as previously explained.

In FIG. 8 is shown a preferred form of opening device for opening a lidof a container. A handle 118 is secured to a tear open portion 105 ofthe lid 106 bounded by a frangible element 112 whereby the frangibleelement may be ruptured and the tear open portion lifted from the wall.In the figure, a container body 104, a lid 106 and an opening device 80are all preferably made from tinplate although other materials such asaluminum can equally well be used. Lid 106 is joined to body 104 by aseamed joint 108. Use of tinplate for both body and lid is advantageousfrom the point of view of cost. Lid 106 is provided with a reinforcedshoulder 110 similar to shoulder 94 above described and a thinnedportion or weakened line 112 to provide a frangible element which isformed in a manner similar to that above described. A folded connection76 provided in the material (see also FIG. 6) secures tabs 78 of theopening device 80 to the lid. The folded connection may be made byclenching downwardly triangular shaped ears formed in the blank prior topressing the weakened line as above described with reference to FIG. 6.The lid has an annular bead 114 similar to the beads 30 and 102previously described in relation to FIGS. 3 and 7, and a stiffening bead116.

The opening device 80 comprises a tab handle 118 including a ring and astiffening bead 120 provided with a nose portion integrally connected totabs 78 by a hinge portion 124. In the initial inoperative position ofthe tab handle in which it lies substantially parallel to that of thelid, the nose portion 122 is located above and inwardly of the thinnedportion or frangible element 112 spanning the bead 114. The nose portion122 is reinforced by folding corners 126 over hinge portion 124 as shownin FIG. 8. Slits 128 one each side of head 120 allow bead 120 to belifted by handle 1.18 so that the hinging can take place and theoverlying corners 126 serve to prevent tearing of the metal along thelines of slits 128 beyond the edges 130 as the handle 118 is lifted. Thereinforcement which the corners 126 provide does not increase theoverall height of the opening device and therefore allowsthe containerlids with their opening devices to be nested prior to assembly oncontainer bodies.

In FIG. 9 the handle 118 is shown lifted to its operative position withnose portion 122 hinging downwardly and breaking through or puncturing aportion of the frangible element 112 so as to bend down an underlyingportion 113 of the lid. The handle with its securing means is thenupwardly pulled out of the original plane of the lid to fracture throughon each side of the initial puncture the remainder of the frangibleelement 112 against the shoulder 110 so lifting and removing the portion105 of the lid inwardly of the element 112 from the container. Intinplate, the lid is preferably so constructed that as the removableportion is lifted by the handle the shearing of the remainder of thefrangible element on each side of the original puncture point proceedswith a minimum amount of bending of the removable portion taking place.It will be understood that this preferred process is different from theaction in tear-off containers previously proposed in which a scored lineis progressively torn through to peel off a from the container aremovable portion of the lid which bends appreciably in the process.

In opening means using a frangible element made by the means hereindescribed, a handle may be secured to a removable portion of thecontainer wall by means other than those above described, e.g., byriveting, welding or other securing means.

In FIG. there is shown a sheet container wall 132 made of tinplatehaving a rim portion 134 and weakened line or frangible element 136. Thefrangible element 136 is bounded on one side by an upward formation inthe form of a step 138 leading to a first portion 140 of the containerwall and on the other side by a downward formation in the other surfaceof the metal leading to a second portion 144, the downward formationbeing in the form of the under surface of a hollow bead 142. Thefrangible element 136 defines a tearopen geometric pattern surrounding atear-open panel 146 and is in this example annular in plan. Thefrangible element 136 is in.the form of a thinned portion of the metalconstituting an area of thickness smaller than the general,substantially uniform thickness of the container wall 132 and iselongated inwardly from the peripheral bounds of the geometric patternrepresented by the step 138, having a controlled section of constantthickness.

I c'ess metal which flows from the frangible element 136 when the metalis thinned to form the weakened line in suitable press forming dies.

Close to the bead 142 is provided in the tear-open panel 146 a series ofdownwardly directed bead formations or indentations 148 with a spaceproviding flat portions 150 between the extremities of the beads 148.Alternatively the beads 148 may be upwardly formed. The beads 148 may besuitably spaced all round the tear-open panel or partly round itadjacent to an opening device, e.g., in the formofa handle (not shown)for removing said tear-open panel 146.

The beads 148 are formed at the dame time as the bead 142 and theformation of the beads by a pressing operation is preferably initiatedbefore the pressing of the element 136 and is continued at the same timeas this element is thinned. It has been found that, when this theillustrated sheet container wall is formed by a pressing operating inthis way, the element 136 can be brought to its thinned-out conditionshown without any production of cracks and without any rupture of thetin surface.

The purpose of the beads 148 apart from assisting to take up excessmetal from the thinned portion is to provide control means for assistingthe removal of the tearopen panel to avoid contents, especially anyliquid contents of the container, from spilling, as can happen when atear-open panel-is tooquickly removed. Beads 148 intermittently stiffenthe parts of the panel so that when said panel is torn out ofthe'container by fracturing frangible element 136 the surface of thepanel beads slightly in a series of hinge-like movements across flatportions 150 along bend lines (shown by dotted lines 152) extendingacross-the panel between successive pairs of beads on either side of thepanel. The beads 148 provide the desired control without increasing thedepth of the lid which is an important factor from the viewpoint of massproduction techniques.

The thickness of the metal may be reduced to less than one half inmaking the frangible element 156. In tinplate the residual thickness mayconveniently be about one third the original thickness of the sheet. Byway of example only, for tinplate of thickness 0.009 in. the depth ofthe residual metal in the frangible element may be 0.003 ins. and thewidth of the frangible element may be 0.002 ins., the width of metal asa whole which has been thinned to below the original thickness being,because of the sloping nature of the upward and downward formations 138and 142 on either side of the frangible element, of a width greater thanthe width and also greater than the thickness of the frangible element.The curves joining the frangible element to the upward and downwardformations in this example may be of 0.004 ins. radius.

FIG. 11 shows alternative means for controlling the rate of opening of atear-open panel. A sheet container wall 154 made of tinplate having arim portion 157 is provided with a weakened line or frangible element156. The frangible element 156 is bounded by an upward formation in theform of a step 158 on one side and by a downward formation 160 in theopposite surface of the metal on the other side and forms part of anextrusion in the metal defining a tear-open panel 162. The frangibleelement 156 is in the form of a thinned annular portion of the metalconstituting an area of thickness smaller than the general,substantially uniform thickness of the container wall 154 and is elon'gated inwardly from the peripheral bounds 158 of the frangible element156 having a controlled section of constant thickness.

The downward formation 160 is constituted by a series of downwardlydirected separate beads or indentations 164 or some such similar shapesand by separate step formations 166 in the underside of the metallinking the beads 164. The beads are so dimensioned that theirconfigurations take up the excess metal which flows from the frangibleelement 156 when this is made in suitable press forming dies. Spaces 168lie between the extremities of the bead formations 164. Beads may beformed all round the periphery of tear-open panel 162 adjacent tofrangible element 156 or may be formed partly round it. Instead of beingdownwardly directed, the beads 164 can in an alternative example beupwardlyformed.

When the tear-open panel is removed from the container by fracturing thefrangible element 156 the surface of the panel bends slightly in aseries of hinge-like movements across flat portions 168 along bend lines170 (shown by dotted lines). In this manner the removing of tear-openpanel is controlled by the successive bending at the bend lines 170which avoids the risk of spilling the contents of the containers whenthese hold liquids or powders.

FIG. 12 shows a part cross-section through a sheet metal container whichhas been fitted with a lid consisting of a sheet metal member of thetype illustrated in FIG. 11, the section being taken along one of thelines 170 of that figure. In order to fit the lid on the cylindricalwall 172 of the container the rim portion 157 of the lid has been foldedinto the top of the wall 172 forming a bead 174 at the top of thecontainer.

A tab handle 176, shown in FIG. 13, has been riveted to the lid by meansof a conventional boss type rivet 180 or by other suitable attachmentmeans. The tab handle 176 is made of tinplate or other suitable materialand has a nose portion 178 and a ring handle 182. To open the containerthe tab handle is lifted towards the rim of the lid causing nose portion178 to penetrate the frangible element 156, breaking through this for ashort distance each side of the nose portion 178 and bending a portionof the lid locally downwards into the container.

The tab handle 176 is next pulled upwardly, fracturing the frangibleelement 156 further round its periphery. As the tear-open panel 162within the element 156 is being removed from the container its surfacebends slightly in a series of hinge-like movements round bend lines 170which form in the panel between successive pairs of beads 164 onopposite sides of the handle as seen in FIG. 13. In this manner theremoval of tear-open panel 162 from the container is controlled by thesuccessive bending at the bend line 170 which avoids the risk ofspilling the contents as can happen when lids of known design are pulledfrom a container.

In FIG. 14 the sheet container wall 188 has a weakened line or frangibleelement 190, annular in plan, bounded on its outer side by an upwardformation 192 and on its inner side by an upward formation 194. A seriesof upwardly formed beads 196 is located within the frangible element190. These beads 196 are further from the frangible element than are thebeads in FIGS. 10 and 11, but are nevertheless close enough to allowflow of metal inwardly during formation of the frangible element, thebeads being formed simultaneously therewith. The beads 196 have exactlythe same function as those of FIGS. 10 and 11, that is to say, when thetear-open panel is torn out of the container, the surface of the panelbends slightly along bend lines 198.

FIG. 15 is a cross-section of the same container wall but showing thebeads 196 in a position so closely adjacent the frangible element 190that the upward formation 194, where it lies opposite a bead 196, leadsdirectly into the outer surface of the bead in an exactly analogousmanner to FIG. 11, except that the beads are upwards instead ofdownwards.

The series of beads in both arrangements is if necessary interruptedadjacent the tab handle or any other attached opening means employed fora sufficient distance to prevent any beadinterfering with the dueopening of the container.

It will be appreciated that the series of upwardly formed beads 196shown in FIGS. 14 and 15 may be replaced by a single upwardly directedbead, equivalent to the bead 142, of FIG. 10 except that it has beenupwardly instead of downwardly formed. FIG. 15 may equally be regardedas a cross-section through such a single upwardly formed bead.

Thinned portions in accordance with this invention may be made tocompletely surround the lid or wall of a container or a portion thereofin the form of a circle or other suitable closed figure, or, if desired,may only partly surround part or the whole of a lid which can then bebent away from or into the container after fracturing the thinnedportion.

The fracturing need not be carried out by handle means and the methodand apparatus of this invention are intended for use in the manufacturegenerally of frangible elements in container walls however these may beutilized.

WHAT IS CLAIMED IS:

1. Sheet material having a first portion, a rounded step in the topsurface of the first portion of the sheet leading to a frangible elementcomprising material of smaller thickness than the first portion, arounded formation in a surface of the sheet leading from the frangibleelement to a second portion of the sheet material, the second portionhaving a thickness greater than that of the frangible element and havingformed therein at least one hollow indentation.

2. Sheet material according to claim 1 wherein the said formation is arounded step.

3. Sheet material according to claim 2 wherein the two steps are in thesame direction and are in opposite surfaces of the material.

4. Sheet material according to claim 1 wherein at least the parts of thefirst and second portions adjacent the frangible element are in parallelplanes.

5. Sheet material according to claim 1 wherein the said roundedformation is a rounded formation in the opposite surface of the sheetfrom the rounded step and in the same direction as the step.

6. Sheet material according to claim 1 wherein the material is tinplate.

7. Sheet material according to claim is a hollow bead in the secondportion adjacent the rounded formation.

8. Sheet material according to claim 7 wherein there is a furtherindentation in the second portion more remote from the roundedformation.

9. Sheet material according to claim 1 wherein the material of the firstand second portion is at least about three times thicker than thematerial of the frangible element.

10. Plated sheet material having a firstportion, a rounded step in thetop surface of the first portion of the sheet leading to a frangibleelement comprising material of smaller thickness than the first portion,a rounded formation in a surface of the sheet leading from the frangibleelement to a second portion of the sheet material, the second portionhaving a thickness greater than that of the frangible element and havingformed therein at least one hollow indentation, the plating on thesurface of the sheet material being unbroken in the region of thefrangible element, the step and the rounded formation.

11. A container wall formed of sheet metal having a thinned portion of awidth greater than its thickness comprising a frangible element boundinga tear-open panel, an elongate deformation in the tear-open panelextending alongside and close to the thinned portion comprisingsubstantially parallel curves in the two surfaces of the tear-openpanel.

12. A container wall according to claim 11 wherein a handle is securedto the tear-open panel of the wall bounded by the thinned portionwhereby said thinned portion may be ruptured and the tear-open panellifted from the wall.

13. A container wall according to claim 12 formed of tinplate whereinthe handle is hinged to allow initial downward puncture of the frangibleelement on lifting the handle. I

14. Sheet material having a first portion, a downward formation in thetop surface of the sheet leading to a frangible element comprisingmaterial of smaller thickness than the first portion, the downwardformation in the bottom surface of the sheet leading from the frangibleelement to a second portion of the sheet material, the second portionhaving a thickness greater than that of the frangible element and havingformed therein a hollow bead close to the frangible element.

15. Sheet material according to claim 14 wherein the first and secondportions of the sheet material are of substantially uniform thicknessand the frangible element has a thickness less than half that of theuniform thickness.

16. Sheet material according to claim 14 comprising a container wallwherein each downward formation forms a closed figure in the wall, onedownward formation lying inwardly of the other and substantially paral-.

lel thereto, the downward formations bounding a frangible element ofsubstantially constant width.

1 wherein there 1 the width of the .frangible element exceeds itsthickness. I

18. Sheet material according to claim 14 wherein the downward formationin the top and bottom surfaces are both in the form of rounded steps, aportion of the sheet material between the steps constituting thefrangible element, the material having a shoulder adjacent one of thesteps on the opposite side thereof from the frangible element the hollowbead in the sheet material being adjacent the other step on the sideopposite from the frangible element.

19. Sheet material according to claim 14 wherein the downward formationsin the top and bottom surfaces are both in the form of rounded steps.

20. Sheet material according to claim 14 formed of tinplate.

21. Sheet metal having a first formation in the top surface of the sheetleading to a frangible element comprising metal of smaller thicknessthan the first portion, a downward formation in the bottom surface ofthe sheet leading from the frangible element to a second portion of thesheet metal of thickness substantially the same as that of the firstportion, an area of the second portion adjoining the thinned portionbeing planar except for a deformation there-in formed betweensubstantially parallel curved depressions in the metal surfaces close tothe thinned portion.

22. Sheet material having a first portion, a downward formation in thetop surface of the sheet leading to a frangible element comprisingmaterial of smaller thickness than the first portion, a second portionof thickness greater than that of the frangible element joining thefrangible element on the other side from the first portion, and aseries-of indentations in the second portion. i

' 23. Sheet material according to claim 22 wherein a single elongatebead is provided in the second portion close to the frangible elementand a series of indentations is provided in the second portion on theopposite side of the single bead from the frangible element.

24. Sheet material according to claim 23 wherein the frangible elementis in the form of a continuous figure in the sheet, and the elongatebead is formed inwardly of and parallel to the frangible element.

25. Sheet material according to claim 23 wherein the said series is aseries of beads parallel to the single elongate bead.

26. Sheet material according to claim 22 wherein a series of heads isformed close to the frangible element.

27. Sheet material according to claim 26 wherein the frangible elementis in the form of a continuous figure in the sheet and the series ofbeads is formed inwardly of and parallel to the frangible element.

28. Sheet material according to claim 22 wherein the indentations are soarranged in the second portion that the sheet material has a pluralityof substantially parallel lines of low resistance to flexing separatedby areas of relatively high resistance to flexing.

29. A container wall formed of sheet material according to claim 22wherein the sheet material may be bent along successive lines across thesheet between the indentations when the frangible element is broken 7through.

portion, a downward downward formations bounding a frangible element ofsubstantially constant width defining a tear-open panel.

1. Sheet material having a first portion, a rounded step in the topsurface of the first portion of the sheet leading to a frangible elementcomprising material of smaller thickness than the first portion, arounded formation in a surface of the sheet leading from the frangibleelement to a second portion of the sheet material, the second portionhaving a thickness greater than that of the frangible element and havingformed therein at least one hollow indentation.
 2. Sheet materialaccording to claim 1 wherein the said formation is a rounded step. 3.Sheet material according to claim 2 wherein the two steps are in thesame direction and are in opposite surfaces of the material.
 4. Sheetmaterial according to claim 1 wherein at least the parts of the firstand second portions adjacent the frangible element are in parallelplanes.
 5. Sheet material according to claim 1 wherein the said roundedformation is a rounded formation in the opposite surface of the sheetfrom the rounded step and in the same direction as the step.
 6. Sheetmaterial according to claim 1 wherein the material is tinplate.
 7. Sheetmaterial according to claim 1 wherein there is a hollow bead in thesecond portion adjacent the rounded formation.
 8. Sheet materialaccording to claim 7 wherein there is a further indentation in thesecond portion more remote from the rounded formation.
 9. Sheet materialaccording to claim 1 wherein the material of the first and secondportion is at least about three times thicker than the material of thefrangible element.
 10. Plated sheet material having a first portion, arounded step in the top surface of the first portion of the sheetleading to a frangible element comprising material of smaller thicknessthan the first portion, a rounded formation in a surface of the sheetleading from the frangible element to a second portion of the sheetmaterial, the second portion having a thickness greater than that of thefrangible element and having formed therein at least one hollowindentation, the plating on the surface of the sheet material beingunbroken in the region of the frangible element, the step and therounded formation.
 11. A container wall formed of sheet metal having athinned portion of a width greater than its thickness comprising afrangible element bounding a tear-open panel, an elongate deformation inthe tear-open panel extending alongside and close to the thinned portioncomprising substantially parallel curves in the two surfaces of thetear-open panel.
 12. A container wall according to claim 11 wherein ahandle is secured to the tear-open panel of the wall bounded by thethinned portion whereby said thinned portion may be ruptured and thetear-open panel lifted from the wall.
 13. A container wall according toclaim 12 formed of tinplate wherein the handle is hinged to allowinitial downward puncture of the frangible element on lifting thehandle.
 14. Sheet material having a first portion, a downward formationin the top surface of the sheet leading to a frangible elementcomprising material of smaller thicknEss than the first portion, thedownward formation in the bottom surface of the sheet leading from thefrangible element to a second portion of the sheet material, the secondportion having a thickness greater than that of the frangible elementand having formed therein a hollow bead close to the frangible element.15. Sheet material according to claim 14 wherein the first and secondportions of the sheet material are of substantially uniform thicknessand the frangible element has a thickness less than half that of theuniform thickness.
 16. Sheet material according to claim 14 comprising acontainer wall wherein each downward formation forms a closed figure inthe wall, one downward formation lying inwardly of the other andsubstantially parallel thereto, the downward formations bounding afrangible element of substantially constant width.
 17. A container wallaccording to claim 16 wherein the width of the frangible element exceedsits thickness.
 18. Sheet material according to claim 14 wherein thedownward formation in the top and bottom surfaces are both in the formof rounded steps, a portion of the sheet material between the stepsconstituting the frangible element, the material having a shoulderadjacent one of the steps on the opposite side thereof from thefrangible element the hollow bead in the sheet material being adjacentthe other step on the side opposite from the frangible element. 19.Sheet material according to claim 14 wherein the downward formations inthe top and bottom surfaces are both in the form of rounded steps. 20.Sheet material according to claim 14 formed of tinplate.
 21. Sheet metalhaving a first portion, a downward formation in the top surface of thesheet leading to a frangible element comprising metal of smallerthickness than the first portion, a downward formation in the bottomsurface of the sheet leading from the frangible element to a secondportion of the sheet metal of thickness substantially the same as thatof the first portion, an area of the second portion adjoining thethinned portion being planar except for a deformation there-in formedbetween substantially parallel curved depressions in the metal surfacesclose to the thinned portion.
 22. Sheet material having a first portion,a downward formation in the top surface of the sheet leading to afrangible element comprising material of smaller thickness than thefirst portion, a second portion of thickness greater than that of thefrangible element joining the frangible element on the other side fromthe first portion, and a series of indentations in the second portion.23. Sheet material according to claim 22 wherein a single elongate beadis provided in the second portion close to the frangible element and aseries of indentations is provided in the second portion on the oppositeside of the single bead from the frangible element.
 24. Sheet materialaccording to claim 23 wherein the frangible element is in the form of acontinuous figure in the sheet, and the elongate bead is formed inwardlyof and parallel to the frangible element.
 25. Sheet material accordingto claim 23 wherein the said series is a series of beads parallel to thesingle elongate bead.
 26. Sheet material according to claim 22 wherein aseries of beads is formed close to the frangible element.
 27. Sheetmaterial according to claim 26 wherein the frangible element is in theform of a continuous figure in the sheet and the series of beads isformed inwardly of and parallel to the frangible element.
 28. Sheetmaterial according to claim 22 wherein the indentations are so arrangedin the second portion that the sheet material has a plurality ofsubstantially parallel lines of low resistance to flexing separated byareas of relatively high resistance to flexing.
 29. A container wallformed of sheet material according to claim 22 wherein the sheetmaterial may be bent along successive lines across the sheet between theindentations when the frangible element is broken through.
 30. Acontainer wall according to claim 29 having a pair of downwardformations each in the form of a closed figure in the wall, one downwardformation lying inwardly of the other and substantially parallel to it,the downward formations bounding a frangible element of substantiallyconstant width defining a tear-open panel.